Lokendra Singh.
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// Writing · Sep 11, 2026 · 2 min read

Floci: great at 5 jobs, risky at 4

awsdevops

Floci is great at 5 jobs and quietly dangerous at 4. Here's the cheat sheet.

Floci is the free, MIT-licensed AWS emulator that hit 24k GitHub stars in about six months, as LocalStack put its free edition behind an auth token. One container on port 4566. Leaving LocalStack's free edition is an image swap.

Use it for

  • Local dev with no AWS account - dummy credentials work, and "hybrid" storage survives restarts.
  • CI integration tests - in-memory mode plus Testcontainers modules (Java, Node, Python) give every run a fresh, isolated AWS.
  • Event-driven flows end to end - S3 events, SNS/SQS fan-out, EventBridge, DynamoDB Streams into Lambda, Step Functions. Lambda runs in real containers.
  • Rehearsing IaC - terraform apply and destroy locally with the standard AWS provider, S3 state backend included. OpenTofu and CDK too.
  • Bedrock apps on a local model - set Bedrock Runtime to "proxy" and Converse calls (tool use included) go to Ollama or any OpenAI-compatible server. Default is a stub.

Don't use it for

  • Proving your IAM is right - by default every request is allowed and signatures aren't checked. Opt-in enforcement doesn't cover bucket or Lambda resource policies yet.
  • Load or scaling tests - Service Quotas returns generous static values; Application Auto Scaling policies are stored but do nothing.
  • Chaos drills - AWS FIS experiments are a control-plane simulation. No faults get injected.
  • The final "will it work on AWS?" check - an early Hacker News tester got S3 listings in reverse alphabetical order. Emulators drift at the edges.

The honest part

  • ~24 ms startup and ~13 MiB idle memory are Floci's own numbers.
  • Lambda, RDS and other container-backed services need the Docker socket.
  • It's young and ships twice a month. Pin a version in CI.

My take

Floci is a fast feedback loop, not a verdict. Run it on every commit; keep one real-AWS test for the verdict. And if coding agents write your infra code, let them loose on Floci, not your account keys.

Where do your AWS tests run today: emulator, mocks, or a real dev account?

Sources